The present invention relates to the formation of circuits on a substrate, specifically to circuit formation using pulsed laser processing, and more particularly to a method or process using pulsed laser processing in thin films on low-temperature substrates, with little accompanying temperature rise in the substrate.
Pulsed laser processing (PLP) typically entails applying short (.about.35 ns) pulses of laser energy (0.1-1 J cm.sup.-2) to silicon or thin films of silicon, in vacuum or a dopant gas atmosphere. Gas-immersion laser doping (GILD) has been extensively developed for use in making shallow, highly doped (&gt;10.sup.20 cm.sup.-3) and activated semiconductor junctions. See K. H. Weiner et al., IEEE Electron Device Lett. 13, 369 (1992). Others have used laser processing to achieve low temperature processing for use in making thin film transistors. See K. Sera et al., IEEE Electron Device Lett. 36, 2868 (1989) and R. Z. Bachrach et al., J. Electron. Mater. 19, 241 (1990).
Various prior techniques for improving the crystallinity of semiconductor films by laser energy and doping the films at various depths with various types and concentrations of dopants are exemplified by U.S. Pat. No. 4,059,461 issued Nov. 22, 1977 to J. C. C. Fan et al.; U.S. Pat. No. 4,309,225 issued Jan. 5, 1982 to J. C. C. Fan et al.; U.S. Pat. No. 4,400,715 issued Aug. 23, 1983 to S. G. Barbes et al.; U.S. Pat. No. 4,719,183 issued Jan. 12, 1988 to M. Maekawa; and U.S. Pat. No. 4,751,193 issued Jun. 14, 1988 to J. J. Myrick.
In these prior development and research efforts to improve crystallinity of amorphous material, substrates of silicon or the so-called high temperature plastic or polymeric materials, such as polyimide (e.g. KAPTON, manufactured by Dupont Corp.) have been used, which are capable of withstanding sustained processing temperatures of higher than 180.degree. C. The high temperature plastics are more expensive, have lower resistance to ultraviolet light, lower strength, and less transparency compared to commercial grade, transparent plastics which are incapable of withstanding sustained processing temperatures of higher than 180.degree. C. Thus, there exists in the state of the art a need for a method of producing films mounted on inexpensive low-temperature, commercial grade plastics. The present invention satisfies this need by providing a method or process for crystallization and doping of amorphous silicon on low-temperature plastic using pulsed energy sources.